Configurational anisotropy in square lattices of interacting cobalt dots

Magnetostatic coupling effects are investigated in square lattices of polycrystalline circular Co dots as a function of dot diameter, spacing, and thickness. We observe a quadratic anisotropy for closely spaced dots when the dot thickness exceeds 15 nm, correlated to a change in the magnetization reversal process from coherent rotation to vortex nucleation/annihilation. To understand the observed anisotropy micromagnetic simulations have been performed which show that vortex nucleation is strongly dependent on the micromagnetic configurations.